Exhaust Gas Heat Exchange, in Particular an Exhaust Gas Cooler for Exhaust Gas Recirculation in a Motor Vehicle

ABSTRACT

The invention relates to an exhaust gas heat exchanger, in particular, to an exhaust gas cooler for exhaust gas recirculation in a motor vehicle comprising heat exchanging conduits which are passed through by exhaust gases, surrounded by a coolant and linked to a distributing and/or collecting chambers comprising a flux guiding device which is provided with the exhaust gas input and output sides and a plurality of channels extending therebetween and inclined to each other

The invention concerns an exhaust gas heat exchanger, in particular an exhaust gas cooler, for exhaust gas recirculation in motor vehicles according to the introductory part of patent claim 1.

Exhaust gas heat exchangers are used on the one hand for heating purposes for heating the coolant and on the other hand for cooling the exhaust gases, that is, as an exhaust gas cooler in exhaust gas recirculation in motor vehicles. Exhaust gas recirculation, called EGR for short, serves, as is known, to lower consumption and reduce emissions. Exhaust gas recirculation systems were known from DE-C 199 06 401, for example. A problem with such exhaust gas heat exchangers, in particular exhaust gas coolers, is soot deposition with diesel exhaust gases in the exhaust gas ducts of the exhaust gas cooler. It was therefore proposed in EP-A 677 715 and in DE-A 195 40 683 for exhaust gas coolers that turbulence devices which prevent soot deposition in the exhaust gas flow be arranged in the exhaust pipes. For this purpose, on the inside of the exhaust gas ducts are strips or projections arranged in a V shape, so-called winglets, which generate specific eddies in the exhaust gas flow. Alternatively, ribs can also be used for this purpose. These measures are, however, not always enough to prevent soot deposits which lead to a reduction of performance of the exhaust gas heat exchanger concerned—with the result that the exhaust gas coolers must be given larger dimensions.

In other known exhaust gas heat exchangers it is provided that a catalytic converter with flow channels parallel to each other is mounted in front of the exhaust gas heat exchanger. Usually the catalytic converter is of cylindrical design and arranged in an exhaust pipe which is also cylindrical. The converter has gases flowing through it rectilinearly in the direction of its axis of symmetry and so extends the exhaust pipe in which the converter is arranged. Associated with this are increased space requirements compared with an exhaust gas heat exchanger without catalyst.

Diesel oxidation catalysts, known by the abbreviation DOC, are known in the exhaust train in motor vehicles. Such catalysts have a metal or ceramic honeycomb body having a plurality of fine exhaust gas channels which are coated with a catalytic substance, e.g. a precious metal such as platinum. In the presence of the catalyst, the hydrocarbons oxidise into carbon dioxide and water where there is an excess of oxygen in the exhaust gas. The structure of such catalysts, e.g. with a matrix of special steel, is described in DE-A 29 24 592 and DE-A 35 43 011. The metal support consists, for example, of one smooth and one corrugated spirally wound strip which is soldered or welded after winding. Then this honeycomb body is coated with a catalytic substance by known methods.

The object of the invention is to provide an exhaust gas heat exchanger with reduced space requirements.

This object is achieved by an exhaust gas heat exchanger having the characteristics of claim 1.

A basic concept of the invention is to integrate the flow conducting device in the exhaust gas heat exchanger in such a way that, by means of the flow conducting device, an exhaust flow is influenced in direction of flow, flow rate, flow cross-sectional area, flow distribution and/or other flow parameters. As a result, for example diversion and/or expansion of flow becomes possible in a space-saving manner.

According to a preferred embodiment the flow channels communicate with each other, for example via apertures in partitions separating the flow channels from each other, so that pressure equalisation between the individual flow channels is ensured and flow distribution is evened out over the flow channels.

According to a preferred embodiment, the heat exchanger channels are distributed at the end face over a surface which is opposite the exhaust gas inlet or outlet surface and particularly preferably is covered thereby. As a result, an exhaust flow is distributed by the flow conducting device directly onto the heat exchanger channels or from the heat exchanger channels onto the flow channels.

Particularly preferably, a distance between the flow conducting device and the heat exchanger channels is made so small that the flow channels and the heat exchanger channels are equally subjected to an even flow distribution.

According to an advantageous embodiment, the flow conducting device goes from a round exhaust gas inlet surface to a quadrangular exhaust gas outlet surface or vice versa, allowing a transition from a round to an angular flow cross-section or vice versa. The angles can also be rounded off in this case.

According to advantageous embodiments, the exhaust gas heat exchanger has any heat exchanger channels, e.g. discs or a tube bundle with exhaust tubes. The exhaust gas heat exchanger can also have a bypass channel with exhaust gas valve.

Advantageously, the flow conducting device is integrated in the exhaust gas heat exchanger, i.e. forms part of the exhaust gas heat exchanger. Hence this integrated unit can be prefabricated and inserted in an exhaust pipe, which facilitates assembly. Particularly advantageously, the flow conducting device is arranged inside the inlet connection piece, gaining the advantage of an extremely short length because the flow conducting device is inserted in an existing space in the exhaust gas heat exchanger.

According to a further advantageous embodiment of the invention, the exhaust gas heat exchanger is arranged in an EGR pipe which is connected to the exhaust pipe of the engine either in front of or behind an exhaust turbine. This results in different exhaust gas temperatures upon entering the exhaust gas heat exchanger.

A density of flow channels in the cross-section is, for example, 100 to 600, preferably 150 to 300 per square inch. The flow channels are, for example, 15 to 100, preferably up to 80, particularly preferably 30 to 40 mm long. The flow channels are preferably coated with platinum, in particular with a density of 20 to 320, in particular 40 to 200 or 250 grammes per cubic foot.

The exhaust gas outlet surface is preferably 30 to 150%, particularly preferably 80 to 110% of a cross-sectional area of a heat exchanger block formed by the heat exchanger channels. A pressure loss of the flow conducting device is preferably less than 100%, particularly preferably less than 50%, especially less than 30%, particularly advantageously 5 to 20% of a pressure loss of the heat exchanger channels all together.

According to a preferred embodiment, in particular a liquid coolant can flow round the heat exchanger channels. Preferably, the exhaust gas heat exchanger has a jacket for conducting the coolant, the jacket preferably having an inlet connection piece and an outlet connection piece for the coolant.

According to an advantageous variant, the heat exchanger channels can be cooled by a gaseous coolant, in particular cooling air.

Practical examples of the invention are shown in the drawings and described in more detail below. The figures show:

FIG. 1 schematically a first embodiment of the invention,

FIG. 2 schematically a second embodiment,

FIG. 3 a schematic detail of a third embodiment,

FIG. 4 a schematic detail of a fourth embodiment,

FIG. 5 a schematic cross-section of a fifth embodiment,

FIG. 6 a schematic cross-section of a sixth embodiment, and

FIG. 7 schematically an exhaust gas recirculation system.

FIG. 1 shows an exhaust gas heat exchanger 110 having heat exchanger channels, not shown in detail, which are combined in a heat exchanger block 120, for example a pipe bundle. The heat exchanger channels lead on the inflow side into a distributing chamber 130 in which is arranged a flow conducting device 140 with a planar exhaust gas inlet surface 150 and a planar exhaust gas outlet surface 160 parallel to the exhaust gas inlet surface 150. The distributing chamber 130 is welded or soldered to the heat exchanger block 120, for example.

A plurality of flow channels 170 extend from the exhaust gas inlet surface 150 to the exhaust gas outlet surface 160. The flow channels 170 are inclined relative to each other, so that a cross-section of an exhaust gas flow entering the exhaust gas heat exchanger 110 from the left in FIG. 1 is increased by means of the flow conducting device 140, the exhaust gas flow advantageously being additionally evened out in the process.

The exhaust gas inlet surface 150 and the exhaust gas outlet surface 160 are round. If the cross-sectional area of the heat exchanger block 120 is angled, a minimum distance is necessary between the exhaust gas outlet surface 160 and the heat exchanger block 120, as the distributing chamber 130 has a transitional region 180 from the round to the angular cross-sectional shape.

FIG. 2 shows an exhaust gas heat exchanger 210 having heat exchanger channels, not shown in detail, which are combined in a heat exchanger block 220, for example a pipe bundle. The heat exchanger channels lead on the inflow side into a distributing chamber 230 in which is arranged a flow conducting device 240 having a planar exhaust gas inlet surface 250 and a planar exhaust gas outlet surface 260 parallel to the exhaust gas inlet surface 250. The distributing chamber 230 is welded or soldered to the heat exchanger block 220, for example.

A plurality of flow channels 270 extend from the exhaust gas inlet surface 250 to the exhaust gas outlet surface 260. The flow channels 270 are partially curved, partially rectilinear and inclined relative to each other, so that a cross-section of an exhaust gas flow entering the exhaust gas heat exchanger 210 from the left in FIG. 2 is increased by means of the flow conducting device 240, the exhaust gas flow advantageously being additionally evened out in the process.

The exhaust gas inlet surface 250 is round and the exhaust gas outlet surface 260 covers the cross-sectional area of the heat exchanger block 220 or of the heat exchanger channels and is for this purpose for example angled. The flow conducting device therefore causes a transition from the round to the angular cross-sectional shape, so that the distance between the exhaust gas outlet surface 260 and the heat exchanger block 220 can be left very small.

FIG. 3 shows an exhaust gas heat exchanger 310 having heat exchanger channels, not shown in detail, which are combined in a heat exchanger block 320, for example a pipe bundle. The heat exchanger channels lead on the inflow side into a distributing chamber 330 in which is arranged a flow conducting device 340 having a planar exhaust gas inlet surface 350 and a planar exhaust gas outlet surface 360 at an angle to the exhaust gas inlet surface 350. The distributing chamber 330 is welded or soldered to the heat exchanger block 320, for example.

A plurality of flow channels 370 extend from the exhaust gas inlet surface 350 to the exhaust gas outlet surface 360. The flow channels 370 are curved and arranged in such a way that a cross-section of an exhaust gas flow entering the exhaust gas heat exchanger 310 from below in FIG. 3 is increased by means of the flow conducting device 340, the exhaust gas flow advantageously being additionally evened out in the process. Furthermore, the flow conducting device 340 causes deflection of the exhaust gas flow.

FIG. 4 shows an exhaust gas heat exchanger 410 having heat exchanger channels, not shown in detail, which are combined in a heat exchanger block 420, for example a pipe bundle. The heat exchanger channels lead on the inflow side into a distributing chamber 430 in which is arranged a flow conducting device 440 having a planar exhaust gas inlet surface 450 and a planar exhaust gas outlet surface 460 at an angle to the exhaust gas inlet surface 450. The distributing chamber 430 is welded or soldered to the heat exchanger block 420, for example.

A plurality of flow channels 470 extend from the exhaust gas inlet surface 450 to the exhaust gas outlet surface 460. The flow channels 470 are parallel to each other, but inclined to surface normals both of the exhaust gas inlet surface 450 and of the exhaust gas outlet surface 460, so that a cross-section of an exhaust gas flow entering the exhaust gas heat exchanger 410 from below in FIG. 4 is deflected and preferably evened out by means of the flow conducting device 440.

FIG. 5 shows an exhaust gas heat exchanger 510 having heat exchanger channels, not shown in detail, which are combined in a heat exchanger block 520, for example a pipe bundle. The heat exchanger channels lead on the inflow side into a distributing chamber 530 in which is arranged a flow conducting device 540 having a cylindrical exhaust gas inlet surface 550 and a cylindrical exhaust gas outlet surface 560 coaxial with the exhaust gas inlet surface 550.

A plurality of flow channels 570 extend in a star shape from the exhaust gas inlet surface 550 to the exhaust gas outlet surface 560. The flow channels 570 are inclined relative to each other due to the star shape, but parallel to surface normals both of the exhaust gas inlet surface 550 and of the exhaust gas outlet surface 560, that is to say, the flow channels 570 in each case lead perpendicularly to the surfaces 550, 560. In order for exhaust gas to act as evenly as possible on the exhaust gas inlet surface 550, it is surrounded by an annular channel 590 through which an exhaust gas flow entering the exhaust gas heat exchanger 510 from below in FIG. 5 is conducted to the flow conducting device 540. In an inner chamber of the flow conducting device, that is, inside the cylinder formed by the exhaust gas outlet surface 560, the exhaust gas is collected and delivered to the heat exchanger channels of the heat exchanger block 520.

FIG. 6 shows an exhaust gas heat exchanger 610 having heat exchanger channels, not shown in detail, which are combined in a heat exchanger block 620, for example a pipe bundle. The heat exchanger channels lead on the inflow side into a distributing chamber 630 in which is arranged a flow conducting device 640 having a cylindrical exhaust gas inlet surface 650 and a cylindrical exhaust gas outlet surface 660 coaxial with the exhaust gas inlet surface 650.

A plurality of flow channels 670 extend in a star shape from the exhaust gas inlet surface 650 to the exhaust gas outlet surface 660. The flow channels 670 are inclined relative to each other and furthermore relative to surface normals both of the exhaust gas inlet surface 650 and of the exhaust gas outlet surface 660, due to the star shape. In order for exhaust gas to act as evenly as possible on the exhaust gas inlet surface 650, it is surrounded by an annular channel 690 through which an exhaust gas flow entering the exhaust gas heat exchanger 610 from below in FIG. 6 is conducted to the flow conducting device 640. In an inner chamber of the flow conducting device, that is, inside the cylinder formed by the exhaust gas outlet surface 660, the exhaust gas is collected and delivered to the heat exchanger channels of the heat exchanger block 620, additional deflection and hence under certain circumstances a reduction of pressure loss being achieved by the inclination of the flow channels 670 to the surface normals of the surfaces 650, 660.

According to practical examples not shown, the distributing chamber is attached to the heat exchanger block by a flange joint.

FIG. 7 shows in a schematic view an exhaust gas recirculation system 20 with a diesel engine 21 with which are associated an intake pipe 22 and an exhaust pipe 23. In the intake pipe 22 is arranged a turbocharger 25 which is driven by an exhaust turbine 24 and which compresses the intake air and delivers it to a boost intercooler 26. The exhaust turbine 24 is arranged in the exhaust pipe 23 and subjected to the exhaust gases of the diesel engine 21. An exhaust gas recirculation pipe 28 having an exhaust gas recirculation valve 29 and an exhaust gas heat exchanger 30 is connected to the exhaust pipe 23 at a branch point 27 and to the intake pipe 22 at connection point 31. The exhaust gas is thus returned in cooled form. Removal of the exhaust gas at branch point 27 therefore takes place in front of the exhaust turbine 24. According to an alternative which is shown by an exhaust gas recirculation pipe 32 shown in broken lines, the exhaust gas is removed at a branch point 33 behind the exhaust turbine 24. The exhaust gas heat exchanger 30 corresponds to the exhaust gas heat exchanger according to the invention described above. Moreover, the exhaust gas heat exchanger 30 can also be designed as an exhaust gas heat exchanger with bypass channel and exhaust gas bypass valve, e.g. according to DE 102 03 003 A1. 

1. Exhaust gas heat exchanger, in particular an exhaust gas cooler, for exhaust gas recirculation in motor vehicles, having heat exchanger channels through which exhaust gas can flow and which lead into a distributing and/or collecting chamber, having a flow conducting device arranged in the distributing and/or collecting chamber, the flow conducting device comprising an exhaust gas inlet surface, an exhaust gas outlet surface and a plurality of flow channels extending from the exhaust gas inlet surface to the exhaust gas outlet surface, wherein the flow channels are inclined relative to each other, the flow channels are inclined relative to a surface normal of the exhaust gas inlet and/or outlet surface, and/or the surface normals of the exhaust gas inlet and outlet surfaces are inclined relative to each other.
 2. Exhaust gas heat exchanger according to claim 1, wherein the flow conducting device is a catalytic converter, in particular oxidation or diesel oxidation catalyst.
 3. Exhaust gas heat exchanger according to claim 1, wherein the flow channels, the exhaust gas inlet surface normal and/or the exhaust gas outlet surface normal are inclined relative to a principal direction of flow of the heat exchanger channels.
 4. Exhaust gas heat exchanger according to claim 1 wherein the flow channels are completely separate from each other.
 5. Exhaust gas heat exchanger according to claim 1, wherein the flow channels communicate with each other via apertures.
 6. Exhaust gas heat exchanger according to claim 1, wherein the exhaust gas outlet surface is as large as the exhaust gas inlet surface.
 7. Exhaust gas heat exchanger according to claim 1, wherein the exhaust gas outlet surface is smaller or larger than the exhaust gas inlet surface.
 8. Exhaust gas heat exchanger according to claim 1 wherein the exhaust gas inlet or outlet surface is opposite the heat exchanger channels and in particular covers all the heat exchanger channels on the outlet or inlet side.
 9. Exhaust gas heat exchanger according to claim 1 wherein a distance between the exhaust gas inlet or outlet surface and the heat exchanger channels is less than 15 mm, preferably less than 10 mm, particularly preferably less than 5 mm.
 10. Exhaust gas heat exchanger according to claim 1, wherein the flow channels are of rectilinear design.
 11. Exhaust gas heat exchanger according to claim 1 wherein the flow channels are of curved design.
 12. Exhaust gas heat exchanger according to claim 1 wherein the exhaust gas inlet and/or outlet surface is round, in particular circular.
 13. Exhaust gas heat exchanger according to claim 1, wherein the exhaust gas inlet and/or outlet surface is angular, in particular quadrangular or rectangular.
 14. Exhaust gas heat exchanger according to claim 1, wherein the exhaust gas inlet and/or outlet surface is curved, in particular cylindrical.
 15. Exhaust gas heat exchanger according to claim 1, wherein the exhaust gas inlet or outlet surface is surrounded by an annular channel for the exhaust gas.
 16. Exhaust gas heat exchanger according to claim 1, wherein the distributing and/or collecting chamber is designed as a diffuser and the flow conducting device in particular fills the diffuser cross-section.
 17. Exhaust gas heat exchanger according to claim 1, wherein the heat exchanger channels are formed by pairs of discs.
 18. Exhaust gas heat exchanger according to claim 1, wherein the heat exchanger channels are formed by tubes which are held with their tube ends in tube bottoms and surrounded by a housing which conducts the coolant.
 19. Exhaust gas heat exchanger according to claim 1, wherein the distributing and/or collecting chamber comprises a flange for connection to an exhaust pipe, in particular to an EGR pipe. 